1 mod manual_saturating_arithmetic;
2 mod option_map_unwrap_or;
3 mod unnecessary_filter_map;
9 use if_chain::if_chain;
12 use rustc::hir::intravisit::{self, Visitor};
13 use rustc::lint::{in_external_macro, LateContext, LateLintPass, Lint, LintArray, LintContext, LintPass};
14 use rustc::ty::{self, Predicate, Ty};
15 use rustc::{declare_lint_pass, declare_tool_lint};
16 use rustc_errors::Applicability;
18 use syntax::source_map::Span;
19 use syntax::symbol::{sym, LocalInternedString};
21 use crate::utils::sugg;
22 use crate::utils::usage::mutated_variables;
24 get_arg_name, get_parent_expr, get_trait_def_id, has_iter_method, implements_trait, in_macro, is_copy,
25 is_ctor_function, is_expn_of, iter_input_pats, last_path_segment, match_def_path, match_qpath, match_trait_method,
26 match_type, match_var, method_calls, method_chain_args, remove_blocks, return_ty, same_tys, single_segment_path,
27 snippet, snippet_with_applicability, snippet_with_macro_callsite, span_lint, span_lint_and_sugg,
28 span_lint_and_then, span_note_and_lint, walk_ptrs_ty, walk_ptrs_ty_depth, SpanlessEq,
30 use crate::utils::{paths, span_help_and_lint};
32 declare_clippy_lint! {
33 /// **What it does:** Checks for `.unwrap()` calls on `Option`s.
35 /// **Why is this bad?** Usually it is better to handle the `None` case, or to
36 /// at least call `.expect(_)` with a more helpful message. Still, for a lot of
37 /// quick-and-dirty code, `unwrap` is a good choice, which is why this lint is
38 /// `Allow` by default.
40 /// **Known problems:** None.
44 /// Using unwrap on an `Option`:
47 /// let opt = Some(1);
54 /// let opt = Some(1);
55 /// opt.expect("more helpful message");
57 pub OPTION_UNWRAP_USED,
59 "using `Option.unwrap()`, which should at least get a better message using `expect()`"
62 declare_clippy_lint! {
63 /// **What it does:** Checks for `.unwrap()` calls on `Result`s.
65 /// **Why is this bad?** `result.unwrap()` will let the thread panic on `Err`
66 /// values. Normally, you want to implement more sophisticated error handling,
67 /// and propagate errors upwards with `try!`.
69 /// Even if you want to panic on errors, not all `Error`s implement good
70 /// messages on display. Therefore, it may be beneficial to look at the places
71 /// where they may get displayed. Activate this lint to do just that.
73 /// **Known problems:** None.
76 /// Using unwrap on an `Option`:
79 /// let res: Result<usize, ()> = Ok(1);
86 /// let res: Result<usize, ()> = Ok(1);
87 /// res.expect("more helpful message");
89 pub RESULT_UNWRAP_USED,
91 "using `Result.unwrap()`, which might be better handled"
94 declare_clippy_lint! {
95 /// **What it does:** Checks for methods that should live in a trait
96 /// implementation of a `std` trait (see [llogiq's blog
97 /// post](http://llogiq.github.io/2015/07/30/traits.html) for further
98 /// information) instead of an inherent implementation.
100 /// **Why is this bad?** Implementing the traits improve ergonomics for users of
101 /// the code, often with very little cost. Also people seeing a `mul(...)`
103 /// may expect `*` to work equally, so you should have good reason to disappoint
106 /// **Known problems:** None.
112 /// fn add(&self, other: &X) -> X {
117 pub SHOULD_IMPLEMENT_TRAIT,
119 "defining a method that should be implementing a std trait"
122 declare_clippy_lint! {
123 /// **What it does:** Checks for methods with certain name prefixes and which
124 /// doesn't match how self is taken. The actual rules are:
126 /// |Prefix |`self` taken |
127 /// |-------|----------------------|
128 /// |`as_` |`&self` or `&mut self`|
130 /// |`into_`|`self` |
131 /// |`is_` |`&self` or none |
132 /// |`to_` |`&self` |
134 /// **Why is this bad?** Consistency breeds readability. If you follow the
135 /// conventions, your users won't be surprised that they, e.g., need to supply a
136 /// mutable reference to a `as_..` function.
138 /// **Known problems:** None.
143 /// fn as_str(self) -> &str {
148 pub WRONG_SELF_CONVENTION,
150 "defining a method named with an established prefix (like \"into_\") that takes `self` with the wrong convention"
153 declare_clippy_lint! {
154 /// **What it does:** This is the same as
155 /// [`wrong_self_convention`](#wrong_self_convention), but for public items.
157 /// **Why is this bad?** See [`wrong_self_convention`](#wrong_self_convention).
159 /// **Known problems:** Actually *renaming* the function may break clients if
160 /// the function is part of the public interface. In that case, be mindful of
161 /// the stability guarantees you've given your users.
167 /// pub fn as_str(self) -> &'a str {
172 pub WRONG_PUB_SELF_CONVENTION,
174 "defining a public method named with an established prefix (like \"into_\") that takes `self` with the wrong convention"
177 declare_clippy_lint! {
178 /// **What it does:** Checks for usage of `ok().expect(..)`.
180 /// **Why is this bad?** Because you usually call `expect()` on the `Result`
181 /// directly to get a better error message.
183 /// **Known problems:** The error type needs to implement `Debug`
187 /// x.ok().expect("why did I do this again?")
191 "using `ok().expect()`, which gives worse error messages than calling `expect` directly on the Result"
194 declare_clippy_lint! {
195 /// **What it does:** Checks for usage of `_.map(_).unwrap_or(_)`.
197 /// **Why is this bad?** Readability, this can be written more concisely as
198 /// `_.map_or(_, _)`.
200 /// **Known problems:** The order of the arguments is not in execution order
204 /// # let x = Some(1);
205 /// x.map(|a| a + 1).unwrap_or(0);
207 pub OPTION_MAP_UNWRAP_OR,
209 "using `Option.map(f).unwrap_or(a)`, which is more succinctly expressed as `map_or(a, f)`"
212 declare_clippy_lint! {
213 /// **What it does:** Checks for usage of `_.map(_).unwrap_or_else(_)`.
215 /// **Why is this bad?** Readability, this can be written more concisely as
216 /// `_.map_or_else(_, _)`.
218 /// **Known problems:** The order of the arguments is not in execution order.
222 /// # let x = Some(1);
223 /// # fn some_function() -> usize { 1 }
224 /// x.map(|a| a + 1).unwrap_or_else(some_function);
226 pub OPTION_MAP_UNWRAP_OR_ELSE,
228 "using `Option.map(f).unwrap_or_else(g)`, which is more succinctly expressed as `map_or_else(g, f)`"
231 declare_clippy_lint! {
232 /// **What it does:** Checks for usage of `result.map(_).unwrap_or_else(_)`.
234 /// **Why is this bad?** Readability, this can be written more concisely as
235 /// `result.ok().map_or_else(_, _)`.
237 /// **Known problems:** None.
241 /// # let x: Result<usize, ()> = Ok(1);
242 /// # fn some_function(foo: ()) -> usize { 1 }
243 /// x.map(|a| a + 1).unwrap_or_else(some_function);
245 pub RESULT_MAP_UNWRAP_OR_ELSE,
247 "using `Result.map(f).unwrap_or_else(g)`, which is more succinctly expressed as `.ok().map_or_else(g, f)`"
250 declare_clippy_lint! {
251 /// **What it does:** Checks for usage of `_.map_or(None, _)`.
253 /// **Why is this bad?** Readability, this can be written more concisely as
256 /// **Known problems:** The order of the arguments is not in execution order.
260 /// opt.map_or(None, |a| a + 1)
262 pub OPTION_MAP_OR_NONE,
264 "using `Option.map_or(None, f)`, which is more succinctly expressed as `and_then(f)`"
267 declare_clippy_lint! {
268 /// **What it does:** Checks for usage of `_.and_then(|x| Some(y))`.
270 /// **Why is this bad?** Readability, this can be written more concisely as
273 /// **Known problems:** None
278 /// let x = Some("foo");
279 /// let _ = x.and_then(|s| Some(s.len()));
282 /// The correct use would be:
285 /// let x = Some("foo");
286 /// let _ = x.map(|s| s.len());
288 pub OPTION_AND_THEN_SOME,
290 "using `Option.and_then(|x| Some(y))`, which is more succinctly expressed as `map(|x| y)`"
293 declare_clippy_lint! {
294 /// **What it does:** Checks for usage of `_.filter(_).next()`.
296 /// **Why is this bad?** Readability, this can be written more concisely as
299 /// **Known problems:** None.
303 /// # let vec = vec![1];
304 /// vec.iter().filter(|x| **x == 0).next();
306 /// Could be written as
308 /// # let vec = vec![1];
309 /// vec.iter().find(|x| **x == 0);
313 "using `filter(p).next()`, which is more succinctly expressed as `.find(p)`"
316 declare_clippy_lint! {
317 /// **What it does:** Checks for usage of `_.map(_).flatten(_)`,
319 /// **Why is this bad?** Readability, this can be written more concisely as a
320 /// single method call.
322 /// **Known problems:**
326 /// let vec = vec![vec![1]];
327 /// vec.iter().map(|x| x.iter()).flatten();
331 "using combinations of `flatten` and `map` which can usually be written as a single method call"
334 declare_clippy_lint! {
335 /// **What it does:** Checks for usage of `_.filter(_).map(_)`,
336 /// `_.filter(_).flat_map(_)`, `_.filter_map(_).flat_map(_)` and similar.
338 /// **Why is this bad?** Readability, this can be written more concisely as a
339 /// single method call.
341 /// **Known problems:** Often requires a condition + Option/Iterator creation
342 /// inside the closure.
346 /// let vec = vec![1];
347 /// vec.iter().filter(|x| **x == 0).map(|x| *x * 2);
351 "using combinations of `filter`, `map`, `filter_map` and `flat_map` which can usually be written as a single method call"
354 declare_clippy_lint! {
355 /// **What it does:** Checks for usage of `_.filter_map(_).next()`.
357 /// **Why is this bad?** Readability, this can be written more concisely as a
358 /// single method call.
360 /// **Known problems:** None
364 /// (0..3).filter_map(|x| if x == 2 { Some(x) } else { None }).next();
366 /// Can be written as
369 /// (0..3).find_map(|x| if x == 2 { Some(x) } else { None });
373 "using combination of `filter_map` and `next` which can usually be written as a single method call"
376 declare_clippy_lint! {
377 /// **What it does:** Checks for usage of `flat_map(|x| x)`.
379 /// **Why is this bad?** Readability, this can be written more concisely by using `flatten`.
381 /// **Known problems:** None
385 /// # let iter = vec![vec![0]].into_iter();
386 /// iter.flat_map(|x| x);
388 /// Can be written as
390 /// # let iter = vec![vec![0]].into_iter();
393 pub FLAT_MAP_IDENTITY,
395 "call to `flat_map` where `flatten` is sufficient"
398 declare_clippy_lint! {
399 /// **What it does:** Checks for usage of `_.find(_).map(_)`.
401 /// **Why is this bad?** Readability, this can be written more concisely as a
402 /// single method call.
404 /// **Known problems:** Often requires a condition + Option/Iterator creation
405 /// inside the closure.
409 /// (0..3).find(|x| *x == 2).map(|x| x * 2);
411 /// Can be written as
413 /// (0..3).find_map(|x| if x == 2 { Some(x * 2) } else { None });
417 "using a combination of `find` and `map` can usually be written as a single method call"
420 declare_clippy_lint! {
421 /// **What it does:** Checks for an iterator search (such as `find()`,
422 /// `position()`, or `rposition()`) followed by a call to `is_some()`.
424 /// **Why is this bad?** Readability, this can be written more concisely as
427 /// **Known problems:** None.
431 /// # let vec = vec![1];
432 /// vec.iter().find(|x| **x == 0).is_some();
434 /// Could be written as
436 /// # let vec = vec![1];
437 /// vec.iter().any(|x| *x == 0);
441 "using an iterator search followed by `is_some()`, which is more succinctly expressed as a call to `any()`"
444 declare_clippy_lint! {
445 /// **What it does:** Checks for usage of `.chars().next()` on a `str` to check
446 /// if it starts with a given char.
448 /// **Why is this bad?** Readability, this can be written more concisely as
449 /// `_.starts_with(_)`.
451 /// **Known problems:** None.
455 /// let name = "foo";
456 /// if name.chars().next() == Some('_') {};
458 /// Could be written as
460 /// let name = "foo";
461 /// if name.starts_with('_') {};
465 "using `.chars().next()` to check if a string starts with a char"
468 declare_clippy_lint! {
469 /// **What it does:** Checks for calls to `.or(foo(..))`, `.unwrap_or(foo(..))`,
470 /// etc., and suggests to use `or_else`, `unwrap_or_else`, etc., or
471 /// `unwrap_or_default` instead.
473 /// **Why is this bad?** The function will always be called and potentially
474 /// allocate an object acting as the default.
476 /// **Known problems:** If the function has side-effects, not calling it will
477 /// change the semantic of the program, but you shouldn't rely on that anyway.
481 /// # let foo = Some(String::new());
482 /// foo.unwrap_or(String::new());
484 /// this can instead be written:
486 /// # let foo = Some(String::new());
487 /// foo.unwrap_or_else(String::new);
491 /// # let foo = Some(String::new());
492 /// foo.unwrap_or_default();
496 "using any `*or` method with a function call, which suggests `*or_else`"
499 declare_clippy_lint! {
500 /// **What it does:** Checks for calls to `.expect(&format!(...))`, `.expect(foo(..))`,
501 /// etc., and suggests to use `unwrap_or_else` instead
503 /// **Why is this bad?** The function will always be called.
505 /// **Known problems:** If the function has side-effects, not calling it will
506 /// change the semantics of the program, but you shouldn't rely on that anyway.
510 /// # let foo = Some(String::new());
511 /// # let err_code = "418";
512 /// # let err_msg = "I'm a teapot";
513 /// foo.expect(&format!("Err {}: {}", err_code, err_msg));
517 /// # let foo = Some(String::new());
518 /// # let err_code = "418";
519 /// # let err_msg = "I'm a teapot";
520 /// foo.expect(format!("Err {}: {}", err_code, err_msg).as_str());
522 /// this can instead be written:
524 /// # let foo = Some(String::new());
525 /// # let err_code = "418";
526 /// # let err_msg = "I'm a teapot";
527 /// foo.unwrap_or_else(|| panic!("Err {}: {}", err_code, err_msg));
531 "using any `expect` method with a function call"
534 declare_clippy_lint! {
535 /// **What it does:** Checks for usage of `.clone()` on a `Copy` type.
537 /// **Why is this bad?** The only reason `Copy` types implement `Clone` is for
538 /// generics, not for using the `clone` method on a concrete type.
540 /// **Known problems:** None.
548 "using `clone` on a `Copy` type"
551 declare_clippy_lint! {
552 /// **What it does:** Checks for usage of `.clone()` on a ref-counted pointer,
553 /// (`Rc`, `Arc`, `rc::Weak`, or `sync::Weak`), and suggests calling Clone via unified
554 /// function syntax instead (e.g., `Rc::clone(foo)`).
556 /// **Why is this bad?** Calling '.clone()' on an Rc, Arc, or Weak
557 /// can obscure the fact that only the pointer is being cloned, not the underlying
562 /// # use std::rc::Rc;
563 /// let x = Rc::new(1);
566 pub CLONE_ON_REF_PTR,
568 "using 'clone' on a ref-counted pointer"
571 declare_clippy_lint! {
572 /// **What it does:** Checks for usage of `.clone()` on an `&&T`.
574 /// **Why is this bad?** Cloning an `&&T` copies the inner `&T`, instead of
575 /// cloning the underlying `T`.
577 /// **Known problems:** None.
584 /// let z = y.clone();
585 /// println!("{:p} {:p}", *y, z); // prints out the same pointer
588 pub CLONE_DOUBLE_REF,
590 "using `clone` on `&&T`"
593 declare_clippy_lint! {
594 /// **What it does:** Checks for `new` not returning `Self`.
596 /// **Why is this bad?** As a convention, `new` methods are used to make a new
597 /// instance of a type.
599 /// **Known problems:** None.
604 /// fn new(..) -> NotAFoo {
610 "not returning `Self` in a `new` method"
613 declare_clippy_lint! {
614 /// **What it does:** Checks for string methods that receive a single-character
615 /// `str` as an argument, e.g., `_.split("x")`.
617 /// **Why is this bad?** Performing these methods using a `char` is faster than
620 /// **Known problems:** Does not catch multi-byte unicode characters.
623 /// `_.split("x")` could be `_.split('x')`
624 pub SINGLE_CHAR_PATTERN,
626 "using a single-character str where a char could be used, e.g., `_.split(\"x\")`"
629 declare_clippy_lint! {
630 /// **What it does:** Checks for getting the inner pointer of a temporary
633 /// **Why is this bad?** The inner pointer of a `CString` is only valid as long
634 /// as the `CString` is alive.
636 /// **Known problems:** None.
640 /// let c_str = CString::new("foo").unwrap().as_ptr();
642 /// call_some_ffi_func(c_str);
645 /// Here `c_str` point to a freed address. The correct use would be:
647 /// let c_str = CString::new("foo").unwrap();
649 /// call_some_ffi_func(c_str.as_ptr());
652 pub TEMPORARY_CSTRING_AS_PTR,
654 "getting the inner pointer of a temporary `CString`"
657 declare_clippy_lint! {
658 /// **What it does:** Checks for use of `.iter().nth()` (and the related
659 /// `.iter_mut().nth()`) on standard library types with O(1) element access.
661 /// **Why is this bad?** `.get()` and `.get_mut()` are more efficient and more
664 /// **Known problems:** None.
668 /// let some_vec = vec![0, 1, 2, 3];
669 /// let bad_vec = some_vec.iter().nth(3);
670 /// let bad_slice = &some_vec[..].iter().nth(3);
672 /// The correct use would be:
674 /// let some_vec = vec![0, 1, 2, 3];
675 /// let bad_vec = some_vec.get(3);
676 /// let bad_slice = &some_vec[..].get(3);
680 "using `.iter().nth()` on a standard library type with O(1) element access"
683 declare_clippy_lint! {
684 /// **What it does:** Checks for use of `.skip(x).next()` on iterators.
686 /// **Why is this bad?** `.nth(x)` is cleaner
688 /// **Known problems:** None.
692 /// let some_vec = vec![0, 1, 2, 3];
693 /// let bad_vec = some_vec.iter().skip(3).next();
694 /// let bad_slice = &some_vec[..].iter().skip(3).next();
696 /// The correct use would be:
698 /// let some_vec = vec![0, 1, 2, 3];
699 /// let bad_vec = some_vec.iter().nth(3);
700 /// let bad_slice = &some_vec[..].iter().nth(3);
704 "using `.skip(x).next()` on an iterator"
707 declare_clippy_lint! {
708 /// **What it does:** Checks for use of `.get().unwrap()` (or
709 /// `.get_mut().unwrap`) on a standard library type which implements `Index`
711 /// **Why is this bad?** Using the Index trait (`[]`) is more clear and more
714 /// **Known problems:** Not a replacement for error handling: Using either
715 /// `.unwrap()` or the Index trait (`[]`) carries the risk of causing a `panic`
716 /// if the value being accessed is `None`. If the use of `.get().unwrap()` is a
717 /// temporary placeholder for dealing with the `Option` type, then this does
718 /// not mitigate the need for error handling. If there is a chance that `.get()`
719 /// will be `None` in your program, then it is advisable that the `None` case
720 /// is handled in a future refactor instead of using `.unwrap()` or the Index
725 /// let mut some_vec = vec![0, 1, 2, 3];
726 /// let last = some_vec.get(3).unwrap();
727 /// *some_vec.get_mut(0).unwrap() = 1;
729 /// The correct use would be:
731 /// let mut some_vec = vec![0, 1, 2, 3];
732 /// let last = some_vec[3];
737 "using `.get().unwrap()` or `.get_mut().unwrap()` when using `[]` would work instead"
740 declare_clippy_lint! {
741 /// **What it does:** Checks for the use of `.extend(s.chars())` where s is a
742 /// `&str` or `String`.
744 /// **Why is this bad?** `.push_str(s)` is clearer
746 /// **Known problems:** None.
751 /// let def = String::from("def");
752 /// let mut s = String::new();
753 /// s.extend(abc.chars());
754 /// s.extend(def.chars());
756 /// The correct use would be:
759 /// let def = String::from("def");
760 /// let mut s = String::new();
762 /// s.push_str(&def);
764 pub STRING_EXTEND_CHARS,
766 "using `x.extend(s.chars())` where s is a `&str` or `String`"
769 declare_clippy_lint! {
770 /// **What it does:** Checks for the use of `.cloned().collect()` on slice to
773 /// **Why is this bad?** `.to_vec()` is clearer
775 /// **Known problems:** None.
779 /// let s = [1, 2, 3, 4, 5];
780 /// let s2: Vec<isize> = s[..].iter().cloned().collect();
782 /// The better use would be:
784 /// let s = [1, 2, 3, 4, 5];
785 /// let s2: Vec<isize> = s.to_vec();
787 pub ITER_CLONED_COLLECT,
789 "using `.cloned().collect()` on slice to create a `Vec`"
792 declare_clippy_lint! {
793 /// **What it does:** Checks for usage of `.chars().last()` or
794 /// `.chars().next_back()` on a `str` to check if it ends with a given char.
796 /// **Why is this bad?** Readability, this can be written more concisely as
797 /// `_.ends_with(_)`.
799 /// **Known problems:** None.
803 /// name.chars().last() == Some('_') || name.chars().next_back() == Some('-')
807 "using `.chars().last()` or `.chars().next_back()` to check if a string ends with a char"
810 declare_clippy_lint! {
811 /// **What it does:** Checks for usage of `.as_ref()` or `.as_mut()` where the
812 /// types before and after the call are the same.
814 /// **Why is this bad?** The call is unnecessary.
816 /// **Known problems:** None.
820 /// # fn do_stuff(x: &[i32]) {}
821 /// let x: &[i32] = &[1, 2, 3, 4, 5];
822 /// do_stuff(x.as_ref());
824 /// The correct use would be:
826 /// # fn do_stuff(x: &[i32]) {}
827 /// let x: &[i32] = &[1, 2, 3, 4, 5];
832 "using `as_ref` where the types before and after the call are the same"
835 declare_clippy_lint! {
836 /// **What it does:** Checks for using `fold` when a more succinct alternative exists.
837 /// Specifically, this checks for `fold`s which could be replaced by `any`, `all`,
838 /// `sum` or `product`.
840 /// **Why is this bad?** Readability.
842 /// **Known problems:** False positive in pattern guards. Will be resolved once
843 /// non-lexical lifetimes are stable.
847 /// let _ = (0..3).fold(false, |acc, x| acc || x > 2);
849 /// This could be written as:
851 /// let _ = (0..3).any(|x| x > 2);
853 pub UNNECESSARY_FOLD,
855 "using `fold` when a more succinct alternative exists"
858 declare_clippy_lint! {
859 /// **What it does:** Checks for `filter_map` calls which could be replaced by `filter` or `map`.
860 /// More specifically it checks if the closure provided is only performing one of the
861 /// filter or map operations and suggests the appropriate option.
863 /// **Why is this bad?** Complexity. The intent is also clearer if only a single
864 /// operation is being performed.
866 /// **Known problems:** None
870 /// let _ = (0..3).filter_map(|x| if x > 2 { Some(x) } else { None });
872 /// As there is no transformation of the argument this could be written as:
874 /// let _ = (0..3).filter(|&x| x > 2);
878 /// let _ = (0..4).filter_map(i32::checked_abs);
880 /// As there is no conditional check on the argument this could be written as:
882 /// let _ = (0..4).map(i32::checked_abs);
884 pub UNNECESSARY_FILTER_MAP,
886 "using `filter_map` when a more succinct alternative exists"
889 declare_clippy_lint! {
890 /// **What it does:** Checks for `into_iter` calls on types which should be replaced by `iter` or
893 /// **Why is this bad?** Arrays and `PathBuf` do not yet have an `into_iter` method which move out
894 /// their content into an iterator. Auto-referencing resolves the `into_iter` call to its reference
895 /// instead, like `<&[T; N] as IntoIterator>::into_iter`, which just iterates over item references
896 /// like calling `iter` would. Furthermore, when the standard library actually
897 /// [implements the `into_iter` method](https://github.com/rust-lang/rust/issues/25725) which moves
898 /// the content out of the array, the original use of `into_iter` got inferred with the wrong type
899 /// and the code will be broken.
901 /// **Known problems:** None
906 /// let _ = [1, 2, 3].into_iter().map(|x| *x).collect::<Vec<u32>>();
908 /// Could be written as:
910 /// let _ = [1, 2, 3].iter().map(|x| *x).collect::<Vec<u32>>();
912 pub INTO_ITER_ON_ARRAY,
914 "using `.into_iter()` on an array"
917 declare_clippy_lint! {
918 /// **What it does:** Checks for `into_iter` calls on references which should be replaced by `iter`
921 /// **Why is this bad?** Readability. Calling `into_iter` on a reference will not move out its
922 /// content into the resulting iterator, which is confusing. It is better just call `iter` or
923 /// `iter_mut` directly.
925 /// **Known problems:** None
930 /// let _ = (&vec![3, 4, 5]).into_iter();
932 pub INTO_ITER_ON_REF,
934 "using `.into_iter()` on a reference"
937 declare_clippy_lint! {
938 /// **What it does:** Checks for calls to `map` followed by a `count`.
940 /// **Why is this bad?** It looks suspicious. Maybe `map` was confused with `filter`.
941 /// If the `map` call is intentional, this should be rewritten.
943 /// **Known problems:** None
948 /// let _ = (0..3).map(|x| x + 2).count();
952 "suspicious usage of map"
955 declare_clippy_lint! {
956 /// **What it does:** Checks for `MaybeUninit::uninit().assume_init()`.
958 /// **Why is this bad?** For most types, this is undefined behavior.
960 /// **Known problems:** For now, we accept empty tuples and tuples / arrays
961 /// of `MaybeUninit`. There may be other types that allow uninitialized
962 /// data, but those are not yet rigorously defined.
968 /// use std::mem::MaybeUninit;
970 /// let _: usize = unsafe { MaybeUninit::uninit().assume_init() };
973 /// Note that the following is OK:
976 /// use std::mem::MaybeUninit;
978 /// let _: [MaybeUninit<bool>; 5] = unsafe {
979 /// MaybeUninit::uninit().assume_init()
982 pub UNINIT_ASSUMED_INIT,
984 "`MaybeUninit::uninit().assume_init()`"
987 declare_clippy_lint! {
988 /// **What it does:** Checks for `.checked_add/sub(x).unwrap_or(MAX/MIN)`.
990 /// **Why is this bad?** These can be written simply with `saturating_add/sub` methods.
995 /// # let y: u32 = 0;
996 /// # let x: u32 = 100;
997 /// let add = x.checked_add(y).unwrap_or(u32::max_value());
998 /// let sub = x.checked_sub(y).unwrap_or(u32::min_value());
1001 /// can be written using dedicated methods for saturating addition/subtraction as:
1004 /// # let y: u32 = 0;
1005 /// # let x: u32 = 100;
1006 /// let add = x.saturating_add(y);
1007 /// let sub = x.saturating_sub(y);
1009 pub MANUAL_SATURATING_ARITHMETIC,
1011 "`.chcked_add/sub(x).unwrap_or(MAX/MIN)`"
1014 declare_lint_pass!(Methods => [
1017 SHOULD_IMPLEMENT_TRAIT,
1018 WRONG_SELF_CONVENTION,
1019 WRONG_PUB_SELF_CONVENTION,
1021 OPTION_MAP_UNWRAP_OR,
1022 OPTION_MAP_UNWRAP_OR_ELSE,
1023 RESULT_MAP_UNWRAP_OR_ELSE,
1025 OPTION_AND_THEN_SOME,
1034 SINGLE_CHAR_PATTERN,
1036 TEMPORARY_CSTRING_AS_PTR,
1046 STRING_EXTEND_CHARS,
1047 ITER_CLONED_COLLECT,
1050 UNNECESSARY_FILTER_MAP,
1054 UNINIT_ASSUMED_INIT,
1055 MANUAL_SATURATING_ARITHMETIC,
1058 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Methods {
1059 #[allow(clippy::cognitive_complexity)]
1060 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx hir::Expr) {
1061 if in_macro(expr.span) {
1065 let (method_names, arg_lists) = method_calls(expr, 2);
1066 let method_names: Vec<LocalInternedString> = method_names.iter().map(|s| s.as_str()).collect();
1067 let method_names: Vec<&str> = method_names.iter().map(std::convert::AsRef::as_ref).collect();
1069 match method_names.as_slice() {
1070 ["unwrap", "get"] => lint_get_unwrap(cx, expr, arg_lists[1], false),
1071 ["unwrap", "get_mut"] => lint_get_unwrap(cx, expr, arg_lists[1], true),
1072 ["unwrap", ..] => lint_unwrap(cx, expr, arg_lists[0]),
1073 ["expect", "ok"] => lint_ok_expect(cx, expr, arg_lists[1]),
1074 ["unwrap_or", "map"] => option_map_unwrap_or::lint(cx, expr, arg_lists[1], arg_lists[0]),
1075 ["unwrap_or_else", "map"] => lint_map_unwrap_or_else(cx, expr, arg_lists[1], arg_lists[0]),
1076 ["map_or", ..] => lint_map_or_none(cx, expr, arg_lists[0]),
1077 ["and_then", ..] => lint_option_and_then_some(cx, expr, arg_lists[0]),
1078 ["next", "filter"] => lint_filter_next(cx, expr, arg_lists[1]),
1079 ["map", "filter"] => lint_filter_map(cx, expr, arg_lists[1], arg_lists[0]),
1080 ["map", "filter_map"] => lint_filter_map_map(cx, expr, arg_lists[1], arg_lists[0]),
1081 ["next", "filter_map"] => lint_filter_map_next(cx, expr, arg_lists[1]),
1082 ["map", "find"] => lint_find_map(cx, expr, arg_lists[1], arg_lists[0]),
1083 ["flat_map", "filter"] => lint_filter_flat_map(cx, expr, arg_lists[1], arg_lists[0]),
1084 ["flat_map", "filter_map"] => lint_filter_map_flat_map(cx, expr, arg_lists[1], arg_lists[0]),
1085 ["flat_map", ..] => lint_flat_map_identity(cx, expr, arg_lists[0]),
1086 ["flatten", "map"] => lint_map_flatten(cx, expr, arg_lists[1]),
1087 ["is_some", "find"] => lint_search_is_some(cx, expr, "find", arg_lists[1], arg_lists[0]),
1088 ["is_some", "position"] => lint_search_is_some(cx, expr, "position", arg_lists[1], arg_lists[0]),
1089 ["is_some", "rposition"] => lint_search_is_some(cx, expr, "rposition", arg_lists[1], arg_lists[0]),
1090 ["extend", ..] => lint_extend(cx, expr, arg_lists[0]),
1091 ["as_ptr", "unwrap"] | ["as_ptr", "expect"] => {
1092 lint_cstring_as_ptr(cx, expr, &arg_lists[1][0], &arg_lists[0][0])
1094 ["nth", "iter"] => lint_iter_nth(cx, expr, arg_lists[1], false),
1095 ["nth", "iter_mut"] => lint_iter_nth(cx, expr, arg_lists[1], true),
1096 ["next", "skip"] => lint_iter_skip_next(cx, expr),
1097 ["collect", "cloned"] => lint_iter_cloned_collect(cx, expr, arg_lists[1]),
1098 ["as_ref"] => lint_asref(cx, expr, "as_ref", arg_lists[0]),
1099 ["as_mut"] => lint_asref(cx, expr, "as_mut", arg_lists[0]),
1100 ["fold", ..] => lint_unnecessary_fold(cx, expr, arg_lists[0]),
1101 ["filter_map", ..] => unnecessary_filter_map::lint(cx, expr, arg_lists[0]),
1102 ["count", "map"] => lint_suspicious_map(cx, expr),
1103 ["assume_init"] => lint_maybe_uninit(cx, &arg_lists[0][0], expr),
1104 ["unwrap_or", arith @ "checked_add"]
1105 | ["unwrap_or", arith @ "checked_sub"]
1106 | ["unwrap_or", arith @ "checked_mul"] => {
1107 manual_saturating_arithmetic::lint(cx, expr, &arg_lists, &arith["checked_".len()..])
1113 hir::ExprKind::MethodCall(ref method_call, ref method_span, ref args) => {
1114 lint_or_fun_call(cx, expr, *method_span, &method_call.ident.as_str(), args);
1115 lint_expect_fun_call(cx, expr, *method_span, &method_call.ident.as_str(), args);
1117 let self_ty = cx.tables.expr_ty_adjusted(&args[0]);
1118 if args.len() == 1 && method_call.ident.name == sym!(clone) {
1119 lint_clone_on_copy(cx, expr, &args[0], self_ty);
1120 lint_clone_on_ref_ptr(cx, expr, &args[0]);
1124 ty::Ref(_, ty, _) if ty.sty == ty::Str => {
1125 for &(method, pos) in &PATTERN_METHODS {
1126 if method_call.ident.name.as_str() == method && args.len() > pos {
1127 lint_single_char_pattern(cx, expr, &args[pos]);
1131 ty::Ref(..) if method_call.ident.name == sym!(into_iter) => {
1132 lint_into_iter(cx, expr, self_ty, *method_span);
1137 hir::ExprKind::Binary(op, ref lhs, ref rhs)
1138 if op.node == hir::BinOpKind::Eq || op.node == hir::BinOpKind::Ne =>
1140 let mut info = BinaryExprInfo {
1144 eq: op.node == hir::BinOpKind::Eq,
1146 lint_binary_expr_with_method_call(cx, &mut info);
1152 fn check_impl_item(&mut self, cx: &LateContext<'a, 'tcx>, impl_item: &'tcx hir::ImplItem) {
1153 if in_external_macro(cx.sess(), impl_item.span) {
1156 let name = impl_item.ident.name.as_str();
1157 let parent = cx.tcx.hir().get_parent_item(impl_item.hir_id);
1158 let item = cx.tcx.hir().expect_item(parent);
1159 let def_id = cx.tcx.hir().local_def_id(item.hir_id);
1160 let ty = cx.tcx.type_of(def_id);
1162 if let hir::ImplItemKind::Method(ref sig, id) = impl_item.node;
1163 if let Some(first_arg) = iter_input_pats(&sig.decl, cx.tcx.hir().body(id)).next();
1164 if let hir::ItemKind::Impl(_, _, _, _, None, _, _) = item.node;
1166 let method_def_id = cx.tcx.hir().local_def_id(impl_item.hir_id);
1167 let method_sig = cx.tcx.fn_sig(method_def_id);
1168 let method_sig = cx.tcx.erase_late_bound_regions(&method_sig);
1170 let first_arg_ty = &method_sig.inputs().iter().next();
1172 // check conventions w.r.t. conversion method names and predicates
1173 if let Some(first_arg_ty) = first_arg_ty;
1176 if cx.access_levels.is_exported(impl_item.hir_id) {
1177 // check missing trait implementations
1178 for &(method_name, n_args, self_kind, out_type, trait_name) in &TRAIT_METHODS {
1179 if name == method_name &&
1180 sig.decl.inputs.len() == n_args &&
1181 out_type.matches(cx, &sig.decl.output) &&
1182 self_kind.matches(cx, ty, first_arg_ty) {
1183 span_lint(cx, SHOULD_IMPLEMENT_TRAIT, impl_item.span, &format!(
1184 "defining a method called `{}` on this type; consider implementing \
1185 the `{}` trait or choosing a less ambiguous name", name, trait_name));
1190 if let Some((ref conv, self_kinds)) = &CONVENTIONS
1192 .find(|(ref conv, _)| conv.check(&name))
1194 if !self_kinds.iter().any(|k| k.matches(cx, ty, first_arg_ty)) {
1195 let lint = if item.vis.node.is_pub() {
1196 WRONG_PUB_SELF_CONVENTION
1198 WRONG_SELF_CONVENTION
1206 "methods called `{}` usually take {}; consider choosing a less \
1211 .map(|k| k.description())
1212 .collect::<Vec<_>>()
1221 if let hir::ImplItemKind::Method(_, _) = impl_item.node {
1222 let ret_ty = return_ty(cx, impl_item.hir_id);
1224 // walk the return type and check for Self (this does not check associated types)
1225 if ret_ty.walk().any(|inner_type| same_tys(cx, ty, inner_type)) {
1229 // if return type is impl trait, check the associated types
1230 if let ty::Opaque(def_id, _) = ret_ty.sty {
1231 // one of the associated types must be Self
1232 for predicate in &cx.tcx.predicates_of(def_id).predicates {
1234 (Predicate::Projection(poly_projection_predicate), _) => {
1235 let binder = poly_projection_predicate.ty();
1236 let associated_type = binder.skip_binder();
1238 // walk the associated type and check for Self
1239 for inner_type in associated_type.walk() {
1240 if same_tys(cx, ty, inner_type) {
1250 if name == "new" && !same_tys(cx, ret_ty, ty) {
1255 "methods called `new` usually return `Self`",
1262 /// Checks for the `OR_FUN_CALL` lint.
1263 #[allow(clippy::too_many_lines)]
1264 fn lint_or_fun_call<'a, 'tcx>(
1265 cx: &LateContext<'a, 'tcx>,
1269 args: &'tcx [hir::Expr],
1271 // Searches an expression for method calls or function calls that aren't ctors
1272 struct FunCallFinder<'a, 'tcx> {
1273 cx: &'a LateContext<'a, 'tcx>,
1277 impl<'a, 'tcx> intravisit::Visitor<'tcx> for FunCallFinder<'a, 'tcx> {
1278 fn visit_expr(&mut self, expr: &'tcx hir::Expr) {
1279 let call_found = match &expr.node {
1280 // ignore enum and struct constructors
1281 hir::ExprKind::Call(..) => !is_ctor_function(self.cx, expr),
1282 hir::ExprKind::MethodCall(..) => true,
1287 // don't lint for constant values
1288 let owner_def = self.cx.tcx.hir().get_parent_did(expr.hir_id);
1289 let promotable = self
1292 .rvalue_promotable_map(owner_def)
1293 .contains(&expr.hir_id.local_id);
1300 intravisit::walk_expr(self, expr);
1304 fn nested_visit_map<'this>(&'this mut self) -> intravisit::NestedVisitorMap<'this, 'tcx> {
1305 intravisit::NestedVisitorMap::None
1309 /// Checks for `unwrap_or(T::new())` or `unwrap_or(T::default())`.
1310 fn check_unwrap_or_default(
1311 cx: &LateContext<'_, '_>,
1314 self_expr: &hir::Expr,
1321 if name == "unwrap_or";
1322 if let hir::ExprKind::Path(ref qpath) = fun.node;
1323 let path = &*last_path_segment(qpath).ident.as_str();
1324 if ["default", "new"].contains(&path);
1325 let arg_ty = cx.tables.expr_ty(arg);
1326 if let Some(default_trait_id) = get_trait_def_id(cx, &paths::DEFAULT_TRAIT);
1327 if implements_trait(cx, arg_ty, default_trait_id, &[]);
1330 let mut applicability = Applicability::MachineApplicable;
1335 &format!("use of `{}` followed by a call to `{}`", name, path),
1338 "{}.unwrap_or_default()",
1339 snippet_with_applicability(cx, self_expr.span, "_", &mut applicability)
1351 /// Checks for `*or(foo())`.
1352 #[allow(clippy::too_many_arguments)]
1353 fn check_general_case<'a, 'tcx>(
1354 cx: &LateContext<'a, 'tcx>,
1358 self_expr: &hir::Expr,
1359 arg: &'tcx hir::Expr,
1363 // (path, fn_has_argument, methods, suffix)
1364 let know_types: &[(&[_], _, &[_], _)] = &[
1365 (&paths::BTREEMAP_ENTRY, false, &["or_insert"], "with"),
1366 (&paths::HASHMAP_ENTRY, false, &["or_insert"], "with"),
1367 (&paths::OPTION, false, &["map_or", "ok_or", "or", "unwrap_or"], "else"),
1368 (&paths::RESULT, true, &["or", "unwrap_or"], "else"),
1372 if know_types.iter().any(|k| k.2.contains(&name));
1374 let mut finder = FunCallFinder { cx: &cx, found: false };
1375 if { finder.visit_expr(&arg); finder.found };
1377 let self_ty = cx.tables.expr_ty(self_expr);
1379 if let Some(&(_, fn_has_arguments, poss, suffix)) =
1380 know_types.iter().find(|&&i| match_type(cx, self_ty, i.0));
1382 if poss.contains(&name);
1385 let sugg: Cow<'_, _> = match (fn_has_arguments, !or_has_args) {
1386 (true, _) => format!("|_| {}", snippet_with_macro_callsite(cx, arg.span, "..")).into(),
1387 (false, false) => format!("|| {}", snippet_with_macro_callsite(cx, arg.span, "..")).into(),
1388 (false, true) => snippet_with_macro_callsite(cx, fun_span, ".."),
1390 let span_replace_word = method_span.with_hi(span.hi());
1395 &format!("use of `{}` followed by a function call", name),
1397 format!("{}_{}({})", name, suffix, sugg),
1398 Applicability::HasPlaceholders,
1404 if args.len() == 2 {
1405 match args[1].node {
1406 hir::ExprKind::Call(ref fun, ref or_args) => {
1407 let or_has_args = !or_args.is_empty();
1408 if !check_unwrap_or_default(cx, name, fun, &args[0], &args[1], or_has_args, expr.span) {
1421 hir::ExprKind::MethodCall(_, span, ref or_args) => check_general_case(
1428 !or_args.is_empty(),
1436 /// Checks for the `EXPECT_FUN_CALL` lint.
1437 #[allow(clippy::too_many_lines)]
1438 fn lint_expect_fun_call(cx: &LateContext<'_, '_>, expr: &hir::Expr, method_span: Span, name: &str, args: &[hir::Expr]) {
1439 // Strip `&`, `as_ref()` and `as_str()` off `arg` until we're left with either a `String` or
1441 fn get_arg_root<'a>(cx: &LateContext<'_, '_>, arg: &'a hir::Expr) -> &'a hir::Expr {
1442 let mut arg_root = arg;
1444 arg_root = match &arg_root.node {
1445 hir::ExprKind::AddrOf(_, expr) => expr,
1446 hir::ExprKind::MethodCall(method_name, _, call_args) => {
1447 if call_args.len() == 1
1448 && (method_name.ident.name == sym!(as_str) || method_name.ident.name == sym!(as_ref))
1450 let arg_type = cx.tables.expr_ty(&call_args[0]);
1451 let base_type = walk_ptrs_ty(arg_type);
1452 base_type.sty == ty::Str || match_type(cx, base_type, &paths::STRING)
1466 // Only `&'static str` or `String` can be used directly in the `panic!`. Other types should be
1467 // converted to string.
1468 fn requires_to_string(cx: &LateContext<'_, '_>, arg: &hir::Expr) -> bool {
1469 let arg_ty = cx.tables.expr_ty(arg);
1470 if match_type(cx, arg_ty, &paths::STRING) {
1473 if let ty::Ref(ty::ReStatic, ty, ..) = arg_ty.sty {
1474 if ty.sty == ty::Str {
1481 fn generate_format_arg_snippet(
1482 cx: &LateContext<'_, '_>,
1484 applicability: &mut Applicability,
1487 if let hir::ExprKind::AddrOf(_, ref format_arg) = a.node;
1488 if let hir::ExprKind::Match(ref format_arg_expr, _, _) = format_arg.node;
1489 if let hir::ExprKind::Tup(ref format_arg_expr_tup) = format_arg_expr.node;
1494 .map(|a| snippet_with_applicability(cx, a.span, "..", applicability).into_owned())
1502 fn is_call(node: &hir::ExprKind) -> bool {
1504 hir::ExprKind::AddrOf(_, expr) => {
1507 hir::ExprKind::Call(..)
1508 | hir::ExprKind::MethodCall(..)
1509 // These variants are debatable or require further examination
1510 | hir::ExprKind::Match(..)
1511 | hir::ExprKind::Block{ .. } => true,
1516 if args.len() != 2 || name != "expect" || !is_call(&args[1].node) {
1520 let receiver_type = cx.tables.expr_ty(&args[0]);
1521 let closure_args = if match_type(cx, receiver_type, &paths::OPTION) {
1523 } else if match_type(cx, receiver_type, &paths::RESULT) {
1529 let arg_root = get_arg_root(cx, &args[1]);
1531 let span_replace_word = method_span.with_hi(expr.span.hi());
1533 let mut applicability = Applicability::MachineApplicable;
1535 //Special handling for `format!` as arg_root
1536 if let hir::ExprKind::Call(ref inner_fun, ref inner_args) = arg_root.node {
1537 if is_expn_of(inner_fun.span, "format").is_some() && inner_args.len() == 1 {
1538 if let hir::ExprKind::Call(_, format_args) = &inner_args[0].node {
1539 let fmt_spec = &format_args[0];
1540 let fmt_args = &format_args[1];
1542 let mut args = vec![snippet(cx, fmt_spec.span, "..").into_owned()];
1544 args.extend(generate_format_arg_snippet(cx, fmt_args, &mut applicability));
1546 let sugg = args.join(", ");
1552 &format!("use of `{}` followed by a function call", name),
1554 format!("unwrap_or_else({} panic!({}))", closure_args, sugg),
1563 let mut arg_root_snippet: Cow<'_, _> = snippet_with_applicability(cx, arg_root.span, "..", &mut applicability);
1564 if requires_to_string(cx, arg_root) {
1565 arg_root_snippet.to_mut().push_str(".to_string()");
1572 &format!("use of `{}` followed by a function call", name),
1574 format!("unwrap_or_else({} {{ panic!({}) }})", closure_args, arg_root_snippet),
1579 /// Checks for the `CLONE_ON_COPY` lint.
1580 fn lint_clone_on_copy(cx: &LateContext<'_, '_>, expr: &hir::Expr, arg: &hir::Expr, arg_ty: Ty<'_>) {
1581 let ty = cx.tables.expr_ty(expr);
1582 if let ty::Ref(_, inner, _) = arg_ty.sty {
1583 if let ty::Ref(_, innermost, _) = inner.sty {
1588 "using `clone` on a double-reference; \
1589 this will copy the reference instead of cloning the inner type",
1591 if let Some(snip) = sugg::Sugg::hir_opt(cx, arg) {
1592 let mut ty = innermost;
1594 while let ty::Ref(_, inner, _) = ty.sty {
1598 let refs: String = iter::repeat('&').take(n + 1).collect();
1599 let derefs: String = iter::repeat('*').take(n).collect();
1600 let explicit = format!("{}{}::clone({})", refs, ty, snip);
1603 "try dereferencing it",
1604 format!("{}({}{}).clone()", refs, derefs, snip.deref()),
1605 Applicability::MaybeIncorrect,
1609 "or try being explicit about what type to clone",
1611 Applicability::MaybeIncorrect,
1616 return; // don't report clone_on_copy
1620 if is_copy(cx, ty) {
1622 if let Some(snippet) = sugg::Sugg::hir_opt(cx, arg) {
1623 let parent = cx.tcx.hir().get_parent_node(expr.hir_id);
1624 match &cx.tcx.hir().get(parent) {
1625 hir::Node::Expr(parent) => match parent.node {
1626 // &*x is a nop, &x.clone() is not
1627 hir::ExprKind::AddrOf(..) |
1628 // (*x).func() is useless, x.clone().func() can work in case func borrows mutably
1629 hir::ExprKind::MethodCall(..) => return,
1632 hir::Node::Stmt(stmt) => {
1633 if let hir::StmtKind::Local(ref loc) = stmt.node {
1634 if let hir::PatKind::Ref(..) = loc.pat.node {
1635 // let ref y = *x borrows x, let ref y = x.clone() does not
1643 // x.clone() might have dereferenced x, possibly through Deref impls
1644 if cx.tables.expr_ty(arg) == ty {
1645 snip = Some(("try removing the `clone` call", format!("{}", snippet)));
1647 let deref_count = cx
1649 .expr_adjustments(arg)
1652 if let ty::adjustment::Adjust::Deref(_) = adj.kind {
1659 let derefs: String = iter::repeat('*').take(deref_count).collect();
1660 snip = Some(("try dereferencing it", format!("{}{}", derefs, snippet)));
1665 span_lint_and_then(cx, CLONE_ON_COPY, expr.span, "using `clone` on a `Copy` type", |db| {
1666 if let Some((text, snip)) = snip {
1667 db.span_suggestion(expr.span, text, snip, Applicability::Unspecified);
1673 fn lint_clone_on_ref_ptr(cx: &LateContext<'_, '_>, expr: &hir::Expr, arg: &hir::Expr) {
1674 let obj_ty = walk_ptrs_ty(cx.tables.expr_ty(arg));
1676 if let ty::Adt(_, subst) = obj_ty.sty {
1677 let caller_type = if match_type(cx, obj_ty, &paths::RC) {
1679 } else if match_type(cx, obj_ty, &paths::ARC) {
1681 } else if match_type(cx, obj_ty, &paths::WEAK_RC) || match_type(cx, obj_ty, &paths::WEAK_ARC) {
1691 "using '.clone()' on a ref-counted pointer",
1694 "{}::<{}>::clone(&{})",
1697 snippet(cx, arg.span, "_")
1699 Applicability::Unspecified, // Sometimes unnecessary ::<_> after Rc/Arc/Weak
1704 fn lint_string_extend(cx: &LateContext<'_, '_>, expr: &hir::Expr, args: &[hir::Expr]) {
1706 if let Some(arglists) = method_chain_args(arg, &["chars"]) {
1707 let target = &arglists[0][0];
1708 let self_ty = walk_ptrs_ty(cx.tables.expr_ty(target));
1709 let ref_str = if self_ty.sty == ty::Str {
1711 } else if match_type(cx, self_ty, &paths::STRING) {
1717 let mut applicability = Applicability::MachineApplicable;
1720 STRING_EXTEND_CHARS,
1722 "calling `.extend(_.chars())`",
1725 "{}.push_str({}{})",
1726 snippet_with_applicability(cx, args[0].span, "_", &mut applicability),
1728 snippet_with_applicability(cx, target.span, "_", &mut applicability)
1735 fn lint_extend(cx: &LateContext<'_, '_>, expr: &hir::Expr, args: &[hir::Expr]) {
1736 let obj_ty = walk_ptrs_ty(cx.tables.expr_ty(&args[0]));
1737 if match_type(cx, obj_ty, &paths::STRING) {
1738 lint_string_extend(cx, expr, args);
1742 fn lint_cstring_as_ptr(cx: &LateContext<'_, '_>, expr: &hir::Expr, source: &hir::Expr, unwrap: &hir::Expr) {
1744 let source_type = cx.tables.expr_ty(source);
1745 if let ty::Adt(def, substs) = source_type.sty;
1746 if match_def_path(cx, def.did, &paths::RESULT);
1747 if match_type(cx, substs.type_at(0), &paths::CSTRING);
1751 TEMPORARY_CSTRING_AS_PTR,
1753 "you are getting the inner pointer of a temporary `CString`",
1755 db.note("that pointer will be invalid outside this expression");
1756 db.span_help(unwrap.span, "assign the `CString` to a variable to extend its lifetime");
1762 fn lint_iter_cloned_collect<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &hir::Expr, iter_args: &'tcx [hir::Expr]) {
1764 if match_type(cx, cx.tables.expr_ty(expr), &paths::VEC);
1765 if let Some(slice) = derefs_to_slice(cx, &iter_args[0], cx.tables.expr_ty(&iter_args[0]));
1766 if let Some(to_replace) = expr.span.trim_start(slice.span.source_callsite());
1771 ITER_CLONED_COLLECT,
1773 "called `iter().cloned().collect()` on a slice to create a `Vec`. Calling `to_vec()` is both faster and \
1776 ".to_vec()".to_string(),
1777 Applicability::MachineApplicable,
1783 fn lint_unnecessary_fold(cx: &LateContext<'_, '_>, expr: &hir::Expr, fold_args: &[hir::Expr]) {
1784 fn check_fold_with_op(
1785 cx: &LateContext<'_, '_>,
1787 fold_args: &[hir::Expr],
1789 replacement_method_name: &str,
1790 replacement_has_args: bool,
1793 // Extract the body of the closure passed to fold
1794 if let hir::ExprKind::Closure(_, _, body_id, _, _) = fold_args[2].node;
1795 let closure_body = cx.tcx.hir().body(body_id);
1796 let closure_expr = remove_blocks(&closure_body.value);
1798 // Check if the closure body is of the form `acc <op> some_expr(x)`
1799 if let hir::ExprKind::Binary(ref bin_op, ref left_expr, ref right_expr) = closure_expr.node;
1800 if bin_op.node == op;
1802 // Extract the names of the two arguments to the closure
1803 if let Some(first_arg_ident) = get_arg_name(&closure_body.params[0].pat);
1804 if let Some(second_arg_ident) = get_arg_name(&closure_body.params[1].pat);
1806 if match_var(&*left_expr, first_arg_ident);
1807 if replacement_has_args || match_var(&*right_expr, second_arg_ident);
1809 if let hir::ExprKind::MethodCall(_, span, _) = &expr.node;
1812 let mut applicability = Applicability::MachineApplicable;
1813 let sugg = if replacement_has_args {
1815 "{replacement}(|{s}| {r})",
1816 replacement = replacement_method_name,
1817 s = second_arg_ident,
1818 r = snippet_with_applicability(cx, right_expr.span, "EXPR", &mut applicability),
1823 replacement = replacement_method_name,
1830 span.with_hi(expr.span.hi()),
1831 // TODO #2371 don't suggest e.g., .any(|x| f(x)) if we can suggest .any(f)
1832 "this `.fold` can be written more succinctly using another method",
1841 // Check that this is a call to Iterator::fold rather than just some function called fold
1842 if !match_trait_method(cx, expr, &paths::ITERATOR) {
1847 fold_args.len() == 3,
1848 "Expected fold_args to have three entries - the receiver, the initial value and the closure"
1851 // Check if the first argument to .fold is a suitable literal
1852 if let hir::ExprKind::Lit(ref lit) = fold_args[1].node {
1854 ast::LitKind::Bool(false) => check_fold_with_op(cx, expr, fold_args, hir::BinOpKind::Or, "any", true),
1855 ast::LitKind::Bool(true) => check_fold_with_op(cx, expr, fold_args, hir::BinOpKind::And, "all", true),
1856 ast::LitKind::Int(0, _) => check_fold_with_op(cx, expr, fold_args, hir::BinOpKind::Add, "sum", false),
1857 ast::LitKind::Int(1, _) => check_fold_with_op(cx, expr, fold_args, hir::BinOpKind::Mul, "product", false),
1863 fn lint_iter_nth<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &hir::Expr, iter_args: &'tcx [hir::Expr], is_mut: bool) {
1864 let mut_str = if is_mut { "_mut" } else { "" };
1865 let caller_type = if derefs_to_slice(cx, &iter_args[0], cx.tables.expr_ty(&iter_args[0])).is_some() {
1867 } else if match_type(cx, cx.tables.expr_ty(&iter_args[0]), &paths::VEC) {
1869 } else if match_type(cx, cx.tables.expr_ty(&iter_args[0]), &paths::VEC_DEQUE) {
1872 return; // caller is not a type that we want to lint
1880 "called `.iter{0}().nth()` on a {1}. Calling `.get{0}()` is both faster and more readable",
1881 mut_str, caller_type
1886 fn lint_get_unwrap<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &hir::Expr, get_args: &'tcx [hir::Expr], is_mut: bool) {
1887 // Note: we don't want to lint `get_mut().unwrap` for HashMap or BTreeMap,
1888 // because they do not implement `IndexMut`
1889 let mut applicability = Applicability::MachineApplicable;
1890 let expr_ty = cx.tables.expr_ty(&get_args[0]);
1891 let get_args_str = if get_args.len() > 1 {
1892 snippet_with_applicability(cx, get_args[1].span, "_", &mut applicability)
1894 return; // not linting on a .get().unwrap() chain or variant
1897 let caller_type = if derefs_to_slice(cx, &get_args[0], expr_ty).is_some() {
1898 needs_ref = get_args_str.parse::<usize>().is_ok();
1900 } else if match_type(cx, expr_ty, &paths::VEC) {
1901 needs_ref = get_args_str.parse::<usize>().is_ok();
1903 } else if match_type(cx, expr_ty, &paths::VEC_DEQUE) {
1904 needs_ref = get_args_str.parse::<usize>().is_ok();
1906 } else if !is_mut && match_type(cx, expr_ty, &paths::HASHMAP) {
1909 } else if !is_mut && match_type(cx, expr_ty, &paths::BTREEMAP) {
1913 return; // caller is not a type that we want to lint
1916 let mut span = expr.span;
1918 // Handle the case where the result is immediately dereferenced
1919 // by not requiring ref and pulling the dereference into the
1923 if let Some(parent) = get_parent_expr(cx, expr);
1924 if let hir::ExprKind::Unary(hir::UnOp::UnDeref, _) = parent.node;
1931 let mut_str = if is_mut { "_mut" } else { "" };
1932 let borrow_str = if !needs_ref {
1945 "called `.get{0}().unwrap()` on a {1}. Using `[]` is more clear and more concise",
1946 mut_str, caller_type
1952 snippet_with_applicability(cx, get_args[0].span, "_", &mut applicability),
1959 fn lint_iter_skip_next(cx: &LateContext<'_, '_>, expr: &hir::Expr) {
1960 // lint if caller of skip is an Iterator
1961 if match_trait_method(cx, expr, &paths::ITERATOR) {
1966 "called `skip(x).next()` on an iterator. This is more succinctly expressed by calling `nth(x)`",
1971 fn derefs_to_slice<'a, 'tcx>(
1972 cx: &LateContext<'a, 'tcx>,
1973 expr: &'tcx hir::Expr,
1975 ) -> Option<&'tcx hir::Expr> {
1976 fn may_slice<'a>(cx: &LateContext<'_, 'a>, ty: Ty<'a>) -> bool {
1978 ty::Slice(_) => true,
1979 ty::Adt(def, _) if def.is_box() => may_slice(cx, ty.boxed_ty()),
1980 ty::Adt(..) => match_type(cx, ty, &paths::VEC),
1981 ty::Array(_, size) => size.eval_usize(cx.tcx, cx.param_env) < 32,
1982 ty::Ref(_, inner, _) => may_slice(cx, inner),
1987 if let hir::ExprKind::MethodCall(ref path, _, ref args) = expr.node {
1988 if path.ident.name == sym!(iter) && may_slice(cx, cx.tables.expr_ty(&args[0])) {
1995 ty::Slice(_) => Some(expr),
1996 ty::Adt(def, _) if def.is_box() && may_slice(cx, ty.boxed_ty()) => Some(expr),
1997 ty::Ref(_, inner, _) => {
1998 if may_slice(cx, inner) {
2009 /// lint use of `unwrap()` for `Option`s and `Result`s
2010 fn lint_unwrap(cx: &LateContext<'_, '_>, expr: &hir::Expr, unwrap_args: &[hir::Expr]) {
2011 let obj_ty = walk_ptrs_ty(cx.tables.expr_ty(&unwrap_args[0]));
2013 let mess = if match_type(cx, obj_ty, &paths::OPTION) {
2014 Some((OPTION_UNWRAP_USED, "an Option", "None"))
2015 } else if match_type(cx, obj_ty, &paths::RESULT) {
2016 Some((RESULT_UNWRAP_USED, "a Result", "Err"))
2021 if let Some((lint, kind, none_value)) = mess {
2027 "used unwrap() on {} value. If you don't want to handle the {} case gracefully, consider \
2028 using expect() to provide a better panic \
2036 /// lint use of `ok().expect()` for `Result`s
2037 fn lint_ok_expect(cx: &LateContext<'_, '_>, expr: &hir::Expr, ok_args: &[hir::Expr]) {
2039 // lint if the caller of `ok()` is a `Result`
2040 if match_type(cx, cx.tables.expr_ty(&ok_args[0]), &paths::RESULT);
2041 let result_type = cx.tables.expr_ty(&ok_args[0]);
2042 if let Some(error_type) = get_error_type(cx, result_type);
2043 if has_debug_impl(error_type, cx);
2050 "called `ok().expect()` on a Result value. You can call `expect` directly on the `Result`",
2056 /// lint use of `map().flatten()` for `Iterators`
2057 fn lint_map_flatten<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx hir::Expr, map_args: &'tcx [hir::Expr]) {
2058 // lint if caller of `.map().flatten()` is an Iterator
2059 if match_trait_method(cx, expr, &paths::ITERATOR) {
2060 let msg = "called `map(..).flatten()` on an `Iterator`. \
2061 This is more succinctly expressed by calling `.flat_map(..)`";
2062 let self_snippet = snippet(cx, map_args[0].span, "..");
2063 let func_snippet = snippet(cx, map_args[1].span, "..");
2064 let hint = format!("{0}.flat_map({1})", self_snippet, func_snippet);
2065 span_lint_and_then(cx, MAP_FLATTEN, expr.span, msg, |db| {
2068 "try using flat_map instead",
2070 Applicability::MachineApplicable,
2076 /// lint use of `map().unwrap_or_else()` for `Option`s and `Result`s
2077 fn lint_map_unwrap_or_else<'a, 'tcx>(
2078 cx: &LateContext<'a, 'tcx>,
2079 expr: &'tcx hir::Expr,
2080 map_args: &'tcx [hir::Expr],
2081 unwrap_args: &'tcx [hir::Expr],
2083 // lint if the caller of `map()` is an `Option`
2084 let is_option = match_type(cx, cx.tables.expr_ty(&map_args[0]), &paths::OPTION);
2085 let is_result = match_type(cx, cx.tables.expr_ty(&map_args[0]), &paths::RESULT);
2087 if is_option || is_result {
2088 // Don't make a suggestion that may fail to compile due to mutably borrowing
2089 // the same variable twice.
2090 let map_mutated_vars = mutated_variables(&map_args[0], cx);
2091 let unwrap_mutated_vars = mutated_variables(&unwrap_args[1], cx);
2092 if let (Some(map_mutated_vars), Some(unwrap_mutated_vars)) = (map_mutated_vars, unwrap_mutated_vars) {
2093 if map_mutated_vars.intersection(&unwrap_mutated_vars).next().is_some() {
2101 let msg = if is_option {
2102 "called `map(f).unwrap_or_else(g)` on an Option value. This can be done more directly by calling \
2103 `map_or_else(g, f)` instead"
2105 "called `map(f).unwrap_or_else(g)` on a Result value. This can be done more directly by calling \
2106 `ok().map_or_else(g, f)` instead"
2108 // get snippets for args to map() and unwrap_or_else()
2109 let map_snippet = snippet(cx, map_args[1].span, "..");
2110 let unwrap_snippet = snippet(cx, unwrap_args[1].span, "..");
2111 // lint, with note if neither arg is > 1 line and both map() and
2112 // unwrap_or_else() have the same span
2113 let multiline = map_snippet.lines().count() > 1 || unwrap_snippet.lines().count() > 1;
2114 let same_span = map_args[1].span.ctxt() == unwrap_args[1].span.ctxt();
2115 if same_span && !multiline {
2119 OPTION_MAP_UNWRAP_OR_ELSE
2121 RESULT_MAP_UNWRAP_OR_ELSE
2127 "replace `map({0}).unwrap_or_else({1})` with `{2}map_or_else({1}, {0})`",
2130 if is_result { "ok()." } else { "" }
2133 } else if same_span && multiline {
2137 OPTION_MAP_UNWRAP_OR_ELSE
2139 RESULT_MAP_UNWRAP_OR_ELSE
2148 /// lint use of `_.map_or(None, _)` for `Option`s
2149 fn lint_map_or_none<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx hir::Expr, map_or_args: &'tcx [hir::Expr]) {
2150 if match_type(cx, cx.tables.expr_ty(&map_or_args[0]), &paths::OPTION) {
2151 // check if the first non-self argument to map_or() is None
2152 let map_or_arg_is_none = if let hir::ExprKind::Path(ref qpath) = map_or_args[1].node {
2153 match_qpath(qpath, &paths::OPTION_NONE)
2158 if map_or_arg_is_none {
2160 let msg = "called `map_or(None, f)` on an Option value. This can be done more directly by calling \
2161 `and_then(f)` instead";
2162 let map_or_self_snippet = snippet(cx, map_or_args[0].span, "..");
2163 let map_or_func_snippet = snippet(cx, map_or_args[2].span, "..");
2164 let hint = format!("{0}.and_then({1})", map_or_self_snippet, map_or_func_snippet);
2165 span_lint_and_then(cx, OPTION_MAP_OR_NONE, expr.span, msg, |db| {
2168 "try using and_then instead",
2170 Applicability::MachineApplicable, // snippet
2177 /// Lint use of `_.and_then(|x| Some(y))` for `Option`s
2178 fn lint_option_and_then_some(cx: &LateContext<'_, '_>, expr: &hir::Expr, args: &[hir::Expr]) {
2179 const LINT_MSG: &str = "using `Option.and_then(|x| Some(y))`, which is more succinctly expressed as `map(|x| y)`";
2180 const NO_OP_MSG: &str = "using `Option.and_then(Some)`, which is a no-op";
2182 // Searches an return expressions in `y` in `_.and_then(|x| Some(y))`, which we don't lint
2183 struct RetCallFinder {
2187 impl<'tcx> intravisit::Visitor<'tcx> for RetCallFinder {
2188 fn visit_expr(&mut self, expr: &'tcx hir::Expr) {
2192 if let hir::ExprKind::Ret(..) = &expr.node {
2195 intravisit::walk_expr(self, expr);
2199 fn nested_visit_map<'this>(&'this mut self) -> intravisit::NestedVisitorMap<'this, 'tcx> {
2200 intravisit::NestedVisitorMap::None
2204 let ty = cx.tables.expr_ty(&args[0]);
2205 if !match_type(cx, ty, &paths::OPTION) {
2209 match args[1].node {
2210 hir::ExprKind::Closure(_, _, body_id, closure_args_span, _) => {
2211 let closure_body = cx.tcx.hir().body(body_id);
2212 let closure_expr = remove_blocks(&closure_body.value);
2214 if let hir::ExprKind::Call(ref some_expr, ref some_args) = closure_expr.node;
2215 if let hir::ExprKind::Path(ref qpath) = some_expr.node;
2216 if match_qpath(qpath, &paths::OPTION_SOME);
2217 if some_args.len() == 1;
2219 let inner_expr = &some_args[0];
2221 let mut finder = RetCallFinder { found: false };
2222 finder.visit_expr(inner_expr);
2227 let some_inner_snip = if inner_expr.span.from_expansion() {
2228 snippet_with_macro_callsite(cx, inner_expr.span, "_")
2230 snippet(cx, inner_expr.span, "_")
2233 let closure_args_snip = snippet(cx, closure_args_span, "..");
2234 let option_snip = snippet(cx, args[0].span, "..");
2235 let note = format!("{}.map({} {})", option_snip, closure_args_snip, some_inner_snip);
2238 OPTION_AND_THEN_SOME,
2243 Applicability::MachineApplicable,
2248 // `_.and_then(Some)` case, which is no-op.
2249 hir::ExprKind::Path(ref qpath) => {
2250 if match_qpath(qpath, &paths::OPTION_SOME) {
2251 let option_snip = snippet(cx, args[0].span, "..");
2252 let note = format!("{}", option_snip);
2255 OPTION_AND_THEN_SOME,
2258 "use the expression directly",
2260 Applicability::MachineApplicable,
2268 /// lint use of `filter().next()` for `Iterators`
2269 fn lint_filter_next<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx hir::Expr, filter_args: &'tcx [hir::Expr]) {
2270 // lint if caller of `.filter().next()` is an Iterator
2271 if match_trait_method(cx, expr, &paths::ITERATOR) {
2272 let msg = "called `filter(p).next()` on an `Iterator`. This is more succinctly expressed by calling \
2273 `.find(p)` instead.";
2274 let filter_snippet = snippet(cx, filter_args[1].span, "..");
2275 if filter_snippet.lines().count() <= 1 {
2276 // add note if not multi-line
2283 &format!("replace `filter({0}).next()` with `find({0})`", filter_snippet),
2286 span_lint(cx, FILTER_NEXT, expr.span, msg);
2291 /// lint use of `filter().map()` for `Iterators`
2292 fn lint_filter_map<'a, 'tcx>(
2293 cx: &LateContext<'a, 'tcx>,
2294 expr: &'tcx hir::Expr,
2295 _filter_args: &'tcx [hir::Expr],
2296 _map_args: &'tcx [hir::Expr],
2298 // lint if caller of `.filter().map()` is an Iterator
2299 if match_trait_method(cx, expr, &paths::ITERATOR) {
2300 let msg = "called `filter(p).map(q)` on an `Iterator`. \
2301 This is more succinctly expressed by calling `.filter_map(..)` instead.";
2302 span_lint(cx, FILTER_MAP, expr.span, msg);
2306 /// lint use of `filter_map().next()` for `Iterators`
2307 fn lint_filter_map_next<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx hir::Expr, filter_args: &'tcx [hir::Expr]) {
2308 if match_trait_method(cx, expr, &paths::ITERATOR) {
2309 let msg = "called `filter_map(p).next()` on an `Iterator`. This is more succinctly expressed by calling \
2310 `.find_map(p)` instead.";
2311 let filter_snippet = snippet(cx, filter_args[1].span, "..");
2312 if filter_snippet.lines().count() <= 1 {
2319 &format!("replace `filter_map({0}).next()` with `find_map({0})`", filter_snippet),
2322 span_lint(cx, FILTER_MAP_NEXT, expr.span, msg);
2327 /// lint use of `find().map()` for `Iterators`
2328 fn lint_find_map<'a, 'tcx>(
2329 cx: &LateContext<'a, 'tcx>,
2330 expr: &'tcx hir::Expr,
2331 _find_args: &'tcx [hir::Expr],
2332 map_args: &'tcx [hir::Expr],
2334 // lint if caller of `.filter().map()` is an Iterator
2335 if match_trait_method(cx, &map_args[0], &paths::ITERATOR) {
2336 let msg = "called `find(p).map(q)` on an `Iterator`. \
2337 This is more succinctly expressed by calling `.find_map(..)` instead.";
2338 span_lint(cx, FIND_MAP, expr.span, msg);
2342 /// lint use of `filter().map()` for `Iterators`
2343 fn lint_filter_map_map<'a, 'tcx>(
2344 cx: &LateContext<'a, 'tcx>,
2345 expr: &'tcx hir::Expr,
2346 _filter_args: &'tcx [hir::Expr],
2347 _map_args: &'tcx [hir::Expr],
2349 // lint if caller of `.filter().map()` is an Iterator
2350 if match_trait_method(cx, expr, &paths::ITERATOR) {
2351 let msg = "called `filter_map(p).map(q)` on an `Iterator`. \
2352 This is more succinctly expressed by only calling `.filter_map(..)` instead.";
2353 span_lint(cx, FILTER_MAP, expr.span, msg);
2357 /// lint use of `filter().flat_map()` for `Iterators`
2358 fn lint_filter_flat_map<'a, 'tcx>(
2359 cx: &LateContext<'a, 'tcx>,
2360 expr: &'tcx hir::Expr,
2361 _filter_args: &'tcx [hir::Expr],
2362 _map_args: &'tcx [hir::Expr],
2364 // lint if caller of `.filter().flat_map()` is an Iterator
2365 if match_trait_method(cx, expr, &paths::ITERATOR) {
2366 let msg = "called `filter(p).flat_map(q)` on an `Iterator`. \
2367 This is more succinctly expressed by calling `.flat_map(..)` \
2368 and filtering by returning an empty Iterator.";
2369 span_lint(cx, FILTER_MAP, expr.span, msg);
2373 /// lint use of `filter_map().flat_map()` for `Iterators`
2374 fn lint_filter_map_flat_map<'a, 'tcx>(
2375 cx: &LateContext<'a, 'tcx>,
2376 expr: &'tcx hir::Expr,
2377 _filter_args: &'tcx [hir::Expr],
2378 _map_args: &'tcx [hir::Expr],
2380 // lint if caller of `.filter_map().flat_map()` is an Iterator
2381 if match_trait_method(cx, expr, &paths::ITERATOR) {
2382 let msg = "called `filter_map(p).flat_map(q)` on an `Iterator`. \
2383 This is more succinctly expressed by calling `.flat_map(..)` \
2384 and filtering by returning an empty Iterator.";
2385 span_lint(cx, FILTER_MAP, expr.span, msg);
2389 /// lint use of `flat_map` for `Iterators` where `flatten` would be sufficient
2390 fn lint_flat_map_identity<'a, 'tcx>(
2391 cx: &LateContext<'a, 'tcx>,
2392 expr: &'tcx hir::Expr,
2393 flat_map_args: &'tcx [hir::Expr],
2395 if match_trait_method(cx, expr, &paths::ITERATOR) {
2396 let arg_node = &flat_map_args[1].node;
2398 let apply_lint = |message: &str| {
2399 if let hir::ExprKind::MethodCall(_, span, _) = &expr.node {
2403 span.with_hi(expr.span.hi()),
2406 "flatten()".to_string(),
2407 Applicability::MachineApplicable,
2413 if let hir::ExprKind::Closure(_, _, body_id, _, _) = arg_node;
2414 let body = cx.tcx.hir().body(*body_id);
2416 if let hir::PatKind::Binding(_, _, binding_ident, _) = body.params[0].pat.node;
2417 if let hir::ExprKind::Path(hir::QPath::Resolved(_, ref path)) = body.value.node;
2419 if path.segments.len() == 1;
2420 if path.segments[0].ident.as_str() == binding_ident.as_str();
2423 apply_lint("called `flat_map(|x| x)` on an `Iterator`");
2428 if let hir::ExprKind::Path(ref qpath) = arg_node;
2430 if match_qpath(qpath, &paths::STD_CONVERT_IDENTITY);
2433 apply_lint("called `flat_map(std::convert::identity)` on an `Iterator`");
2439 /// lint searching an Iterator followed by `is_some()`
2440 fn lint_search_is_some<'a, 'tcx>(
2441 cx: &LateContext<'a, 'tcx>,
2442 expr: &'tcx hir::Expr,
2443 search_method: &str,
2444 search_args: &'tcx [hir::Expr],
2445 is_some_args: &'tcx [hir::Expr],
2447 // lint if caller of search is an Iterator
2448 if match_trait_method(cx, &is_some_args[0], &paths::ITERATOR) {
2450 "called `is_some()` after searching an `Iterator` with {}. This is more succinctly \
2451 expressed by calling `any()`.",
2454 let search_snippet = snippet(cx, search_args[1].span, "..");
2455 if search_snippet.lines().count() <= 1 {
2456 // suggest `any(|x| ..)` instead of `any(|&x| ..)` for `find(|&x| ..).is_some()`
2457 let any_search_snippet = if_chain! {
2458 if search_method == "find";
2459 if let hir::ExprKind::Closure(_, _, body_id, ..) = search_args[1].node;
2460 let closure_body = cx.tcx.hir().body(body_id);
2461 if let Some(closure_arg) = closure_body.params.get(0);
2462 if let hir::PatKind::Ref(..) = closure_arg.pat.node;
2464 Some(search_snippet.replacen('&', "", 1))
2469 // add note if not multi-line
2477 "replace `{0}({1}).is_some()` with `any({2})`",
2480 any_search_snippet.as_ref().map_or(&*search_snippet, String::as_str)
2484 span_lint(cx, SEARCH_IS_SOME, expr.span, &msg);
2489 /// Used for `lint_binary_expr_with_method_call`.
2490 #[derive(Copy, Clone)]
2491 struct BinaryExprInfo<'a> {
2492 expr: &'a hir::Expr,
2493 chain: &'a hir::Expr,
2494 other: &'a hir::Expr,
2498 /// Checks for the `CHARS_NEXT_CMP` and `CHARS_LAST_CMP` lints.
2499 fn lint_binary_expr_with_method_call(cx: &LateContext<'_, '_>, info: &mut BinaryExprInfo<'_>) {
2500 macro_rules! lint_with_both_lhs_and_rhs {
2501 ($func:ident, $cx:expr, $info:ident) => {
2502 if !$func($cx, $info) {
2503 ::std::mem::swap(&mut $info.chain, &mut $info.other);
2504 if $func($cx, $info) {
2511 lint_with_both_lhs_and_rhs!(lint_chars_next_cmp, cx, info);
2512 lint_with_both_lhs_and_rhs!(lint_chars_last_cmp, cx, info);
2513 lint_with_both_lhs_and_rhs!(lint_chars_next_cmp_with_unwrap, cx, info);
2514 lint_with_both_lhs_and_rhs!(lint_chars_last_cmp_with_unwrap, cx, info);
2517 /// Wrapper fn for `CHARS_NEXT_CMP` and `CHARS_LAST_CMP` lints.
2519 cx: &LateContext<'_, '_>,
2520 info: &BinaryExprInfo<'_>,
2521 chain_methods: &[&str],
2522 lint: &'static Lint,
2526 if let Some(args) = method_chain_args(info.chain, chain_methods);
2527 if let hir::ExprKind::Call(ref fun, ref arg_char) = info.other.node;
2528 if arg_char.len() == 1;
2529 if let hir::ExprKind::Path(ref qpath) = fun.node;
2530 if let Some(segment) = single_segment_path(qpath);
2531 if segment.ident.name == sym!(Some);
2533 let mut applicability = Applicability::MachineApplicable;
2534 let self_ty = walk_ptrs_ty(cx.tables.expr_ty_adjusted(&args[0][0]));
2536 if self_ty.sty != ty::Str {
2544 &format!("you should use the `{}` method", suggest),
2546 format!("{}{}.{}({})",
2547 if info.eq { "" } else { "!" },
2548 snippet_with_applicability(cx, args[0][0].span, "_", &mut applicability),
2550 snippet_with_applicability(cx, arg_char[0].span, "_", &mut applicability)),
2561 /// Checks for the `CHARS_NEXT_CMP` lint.
2562 fn lint_chars_next_cmp<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, info: &BinaryExprInfo<'_>) -> bool {
2563 lint_chars_cmp(cx, info, &["chars", "next"], CHARS_NEXT_CMP, "starts_with")
2566 /// Checks for the `CHARS_LAST_CMP` lint.
2567 fn lint_chars_last_cmp<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, info: &BinaryExprInfo<'_>) -> bool {
2568 if lint_chars_cmp(cx, info, &["chars", "last"], CHARS_LAST_CMP, "ends_with") {
2571 lint_chars_cmp(cx, info, &["chars", "next_back"], CHARS_LAST_CMP, "ends_with")
2575 /// Wrapper fn for `CHARS_NEXT_CMP` and `CHARS_LAST_CMP` lints with `unwrap()`.
2576 fn lint_chars_cmp_with_unwrap<'a, 'tcx>(
2577 cx: &LateContext<'a, 'tcx>,
2578 info: &BinaryExprInfo<'_>,
2579 chain_methods: &[&str],
2580 lint: &'static Lint,
2584 if let Some(args) = method_chain_args(info.chain, chain_methods);
2585 if let hir::ExprKind::Lit(ref lit) = info.other.node;
2586 if let ast::LitKind::Char(c) = lit.node;
2588 let mut applicability = Applicability::MachineApplicable;
2593 &format!("you should use the `{}` method", suggest),
2595 format!("{}{}.{}('{}')",
2596 if info.eq { "" } else { "!" },
2597 snippet_with_applicability(cx, args[0][0].span, "_", &mut applicability),
2610 /// Checks for the `CHARS_NEXT_CMP` lint with `unwrap()`.
2611 fn lint_chars_next_cmp_with_unwrap<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, info: &BinaryExprInfo<'_>) -> bool {
2612 lint_chars_cmp_with_unwrap(cx, info, &["chars", "next", "unwrap"], CHARS_NEXT_CMP, "starts_with")
2615 /// Checks for the `CHARS_LAST_CMP` lint with `unwrap()`.
2616 fn lint_chars_last_cmp_with_unwrap<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, info: &BinaryExprInfo<'_>) -> bool {
2617 if lint_chars_cmp_with_unwrap(cx, info, &["chars", "last", "unwrap"], CHARS_LAST_CMP, "ends_with") {
2620 lint_chars_cmp_with_unwrap(cx, info, &["chars", "next_back", "unwrap"], CHARS_LAST_CMP, "ends_with")
2624 /// lint for length-1 `str`s for methods in `PATTERN_METHODS`
2625 fn lint_single_char_pattern<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, _expr: &'tcx hir::Expr, arg: &'tcx hir::Expr) {
2627 if let hir::ExprKind::Lit(lit) = &arg.node;
2628 if let ast::LitKind::Str(r, style) = lit.node;
2629 if r.as_str().len() == 1;
2631 let mut applicability = Applicability::MachineApplicable;
2632 let snip = snippet_with_applicability(cx, arg.span, "..", &mut applicability);
2633 let ch = if let ast::StrStyle::Raw(nhash) = style {
2634 let nhash = nhash as usize;
2635 // for raw string: r##"a"##
2636 &snip[(nhash + 2)..(snip.len() - 1 - nhash)]
2638 // for regular string: "a"
2639 &snip[1..(snip.len() - 1)]
2641 let hint = format!("'{}'", if ch == "'" { "\\'" } else { ch });
2644 SINGLE_CHAR_PATTERN,
2646 "single-character string constant used as pattern",
2647 "try using a char instead",
2655 /// Checks for the `USELESS_ASREF` lint.
2656 fn lint_asref(cx: &LateContext<'_, '_>, expr: &hir::Expr, call_name: &str, as_ref_args: &[hir::Expr]) {
2657 // when we get here, we've already checked that the call name is "as_ref" or "as_mut"
2658 // check if the call is to the actual `AsRef` or `AsMut` trait
2659 if match_trait_method(cx, expr, &paths::ASREF_TRAIT) || match_trait_method(cx, expr, &paths::ASMUT_TRAIT) {
2660 // check if the type after `as_ref` or `as_mut` is the same as before
2661 let recvr = &as_ref_args[0];
2662 let rcv_ty = cx.tables.expr_ty(recvr);
2663 let res_ty = cx.tables.expr_ty(expr);
2664 let (base_res_ty, res_depth) = walk_ptrs_ty_depth(res_ty);
2665 let (base_rcv_ty, rcv_depth) = walk_ptrs_ty_depth(rcv_ty);
2666 if base_rcv_ty == base_res_ty && rcv_depth >= res_depth {
2667 // allow the `as_ref` or `as_mut` if it is followed by another method call
2669 if let Some(parent) = get_parent_expr(cx, expr);
2670 if let hir::ExprKind::MethodCall(_, ref span, _) = parent.node;
2671 if span != &expr.span;
2677 let mut applicability = Applicability::MachineApplicable;
2682 &format!("this call to `{}` does nothing", call_name),
2684 snippet_with_applicability(cx, recvr.span, "_", &mut applicability).to_string(),
2691 fn ty_has_iter_method(
2692 cx: &LateContext<'_, '_>,
2693 self_ref_ty: Ty<'_>,
2694 ) -> Option<(&'static Lint, &'static str, &'static str)> {
2695 has_iter_method(cx, self_ref_ty).map(|ty_name| {
2696 let lint = if ty_name == "array" || ty_name == "PathBuf" {
2701 let mutbl = match self_ref_ty.sty {
2702 ty::Ref(_, _, mutbl) => mutbl,
2703 _ => unreachable!(),
2705 let method_name = match mutbl {
2706 hir::MutImmutable => "iter",
2707 hir::MutMutable => "iter_mut",
2709 (lint, ty_name, method_name)
2713 fn lint_into_iter(cx: &LateContext<'_, '_>, expr: &hir::Expr, self_ref_ty: Ty<'_>, method_span: Span) {
2714 if !match_trait_method(cx, expr, &paths::INTO_ITERATOR) {
2717 if let Some((lint, kind, method_name)) = ty_has_iter_method(cx, self_ref_ty) {
2723 "this .into_iter() call is equivalent to .{}() and will not move the {}",
2727 method_name.to_string(),
2728 Applicability::MachineApplicable,
2733 /// lint for `MaybeUninit::uninit().assume_init()` (we already have the latter)
2734 fn lint_maybe_uninit(cx: &LateContext<'_, '_>, expr: &hir::Expr, outer: &hir::Expr) {
2736 if let hir::ExprKind::Call(ref callee, ref args) = expr.node;
2738 if let hir::ExprKind::Path(ref path) = callee.node;
2739 if match_qpath(path, &paths::MEM_MAYBEUNINIT_UNINIT);
2740 if !is_maybe_uninit_ty_valid(cx, cx.tables.expr_ty_adjusted(outer));
2744 UNINIT_ASSUMED_INIT,
2746 "this call for this type may be undefined behavior"
2752 fn is_maybe_uninit_ty_valid(cx: &LateContext<'_, '_>, ty: Ty<'_>) -> bool {
2754 ty::Array(ref component, _) => is_maybe_uninit_ty_valid(cx, component),
2755 ty::Tuple(ref types) => types.types().all(|ty| is_maybe_uninit_ty_valid(cx, ty)),
2756 ty::Adt(ref adt, _) => {
2757 // needs to be a MaybeUninit
2758 match_def_path(cx, adt.did, &paths::MEM_MAYBEUNINIT)
2764 fn lint_suspicious_map(cx: &LateContext<'_, '_>, expr: &hir::Expr) {
2769 "this call to `map()` won't have an effect on the call to `count()`",
2770 "make sure you did not confuse `map` with `filter`",
2774 /// Given a `Result<T, E>` type, return its error type (`E`).
2775 fn get_error_type<'a>(cx: &LateContext<'_, '_>, ty: Ty<'a>) -> Option<Ty<'a>> {
2777 ty::Adt(_, substs) if match_type(cx, ty, &paths::RESULT) => substs.types().nth(1),
2782 /// This checks whether a given type is known to implement Debug.
2783 fn has_debug_impl<'a, 'b>(ty: Ty<'a>, cx: &LateContext<'b, 'a>) -> bool {
2784 match cx.tcx.get_diagnostic_item(sym::debug_trait) {
2785 Some(debug) => implements_trait(cx, ty, debug, &[]),
2792 StartsWith(&'static str),
2796 const CONVENTIONS: [(Convention, &[SelfKind]); 7] = [
2797 (Convention::Eq("new"), &[SelfKind::No]),
2798 (Convention::StartsWith("as_"), &[SelfKind::Ref, SelfKind::RefMut]),
2799 (Convention::StartsWith("from_"), &[SelfKind::No]),
2800 (Convention::StartsWith("into_"), &[SelfKind::Value]),
2801 (Convention::StartsWith("is_"), &[SelfKind::Ref, SelfKind::No]),
2802 (Convention::Eq("to_mut"), &[SelfKind::RefMut]),
2803 (Convention::StartsWith("to_"), &[SelfKind::Ref]),
2807 const TRAIT_METHODS: [(&str, usize, SelfKind, OutType, &str); 30] = [
2808 ("add", 2, SelfKind::Value, OutType::Any, "std::ops::Add"),
2809 ("as_mut", 1, SelfKind::RefMut, OutType::Ref, "std::convert::AsMut"),
2810 ("as_ref", 1, SelfKind::Ref, OutType::Ref, "std::convert::AsRef"),
2811 ("bitand", 2, SelfKind::Value, OutType::Any, "std::ops::BitAnd"),
2812 ("bitor", 2, SelfKind::Value, OutType::Any, "std::ops::BitOr"),
2813 ("bitxor", 2, SelfKind::Value, OutType::Any, "std::ops::BitXor"),
2814 ("borrow", 1, SelfKind::Ref, OutType::Ref, "std::borrow::Borrow"),
2815 ("borrow_mut", 1, SelfKind::RefMut, OutType::Ref, "std::borrow::BorrowMut"),
2816 ("clone", 1, SelfKind::Ref, OutType::Any, "std::clone::Clone"),
2817 ("cmp", 2, SelfKind::Ref, OutType::Any, "std::cmp::Ord"),
2818 ("default", 0, SelfKind::No, OutType::Any, "std::default::Default"),
2819 ("deref", 1, SelfKind::Ref, OutType::Ref, "std::ops::Deref"),
2820 ("deref_mut", 1, SelfKind::RefMut, OutType::Ref, "std::ops::DerefMut"),
2821 ("div", 2, SelfKind::Value, OutType::Any, "std::ops::Div"),
2822 ("drop", 1, SelfKind::RefMut, OutType::Unit, "std::ops::Drop"),
2823 ("eq", 2, SelfKind::Ref, OutType::Bool, "std::cmp::PartialEq"),
2824 ("from_iter", 1, SelfKind::No, OutType::Any, "std::iter::FromIterator"),
2825 ("from_str", 1, SelfKind::No, OutType::Any, "std::str::FromStr"),
2826 ("hash", 2, SelfKind::Ref, OutType::Unit, "std::hash::Hash"),
2827 ("index", 2, SelfKind::Ref, OutType::Ref, "std::ops::Index"),
2828 ("index_mut", 2, SelfKind::RefMut, OutType::Ref, "std::ops::IndexMut"),
2829 ("into_iter", 1, SelfKind::Value, OutType::Any, "std::iter::IntoIterator"),
2830 ("mul", 2, SelfKind::Value, OutType::Any, "std::ops::Mul"),
2831 ("neg", 1, SelfKind::Value, OutType::Any, "std::ops::Neg"),
2832 ("next", 1, SelfKind::RefMut, OutType::Any, "std::iter::Iterator"),
2833 ("not", 1, SelfKind::Value, OutType::Any, "std::ops::Not"),
2834 ("rem", 2, SelfKind::Value, OutType::Any, "std::ops::Rem"),
2835 ("shl", 2, SelfKind::Value, OutType::Any, "std::ops::Shl"),
2836 ("shr", 2, SelfKind::Value, OutType::Any, "std::ops::Shr"),
2837 ("sub", 2, SelfKind::Value, OutType::Any, "std::ops::Sub"),
2841 const PATTERN_METHODS: [(&str, usize); 17] = [
2849 ("split_terminator", 1),
2850 ("rsplit_terminator", 1),
2855 ("match_indices", 1),
2856 ("rmatch_indices", 1),
2857 ("trim_start_matches", 1),
2858 ("trim_end_matches", 1),
2861 #[derive(Clone, Copy, PartialEq, Debug)]
2870 fn matches<'a>(self, cx: &LateContext<'_, 'a>, parent_ty: Ty<'a>, ty: Ty<'a>) -> bool {
2871 fn matches_value(parent_ty: Ty<'_>, ty: Ty<'_>) -> bool {
2872 if ty == parent_ty {
2874 } else if ty.is_box() {
2875 ty.boxed_ty() == parent_ty
2876 } else if ty.is_rc() || ty.is_arc() {
2877 if let ty::Adt(_, substs) = ty.sty {
2878 substs.types().next().map_or(false, |t| t == parent_ty)
2888 cx: &LateContext<'_, 'a>,
2889 mutability: hir::Mutability,
2893 if let ty::Ref(_, t, m) = ty.sty {
2894 return m == mutability && t == parent_ty;
2897 let trait_path = match mutability {
2898 hir::Mutability::MutImmutable => &paths::ASREF_TRAIT,
2899 hir::Mutability::MutMutable => &paths::ASMUT_TRAIT,
2902 let trait_def_id = match get_trait_def_id(cx, trait_path) {
2904 None => return false,
2906 implements_trait(cx, ty, trait_def_id, &[parent_ty.into()])
2910 Self::Value => matches_value(parent_ty, ty),
2912 matches_ref(cx, hir::Mutability::MutImmutable, parent_ty, ty) || ty == parent_ty && is_copy(cx, ty)
2914 Self::RefMut => matches_ref(cx, hir::Mutability::MutMutable, parent_ty, ty),
2915 Self::No => ty != parent_ty,
2919 fn description(self) -> &'static str {
2921 Self::Value => "self by value",
2922 Self::Ref => "self by reference",
2923 Self::RefMut => "self by mutable reference",
2924 Self::No => "no self",
2930 fn check(&self, other: &str) -> bool {
2932 Self::Eq(this) => this == other,
2933 Self::StartsWith(this) => other.starts_with(this) && this != other,
2938 impl fmt::Display for Convention {
2939 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
2941 Self::Eq(this) => this.fmt(f),
2942 Self::StartsWith(this) => this.fmt(f).and_then(|_| '*'.fmt(f)),
2947 #[derive(Clone, Copy)]
2956 fn matches(self, cx: &LateContext<'_, '_>, ty: &hir::FunctionRetTy) -> bool {
2957 let is_unit = |ty: &hir::Ty| SpanlessEq::new(cx).eq_ty_kind(&ty.node, &hir::TyKind::Tup(vec![].into()));
2959 (Self::Unit, &hir::DefaultReturn(_)) => true,
2960 (Self::Unit, &hir::Return(ref ty)) if is_unit(ty) => true,
2961 (Self::Bool, &hir::Return(ref ty)) if is_bool(ty) => true,
2962 (Self::Any, &hir::Return(ref ty)) if !is_unit(ty) => true,
2963 (Self::Ref, &hir::Return(ref ty)) => matches!(ty.node, hir::TyKind::Rptr(_, _)),
2969 fn is_bool(ty: &hir::Ty) -> bool {
2970 if let hir::TyKind::Path(ref p) = ty.node {
2971 match_qpath(p, &["bool"])